Noncharacters U+FFFF and U+FFFE are not invalid.

Properly decode them and accept to encode them.

This was clarified by Unicode Technical Committee:
http://www.unicode.org/versions/corrigendum9.html

c_src/utf8.c

@@ -62,7 +62,7 @@ utf8_len(int c)
     } else if(c < 0x800) {
         return 2;
     } else if(c < 0x10000) {
-        if(c < 0xD800 || (c > 0xDFFF && c < 0xFFFE)) {
+        if(c < 0xD800 || (c > 0xDFFF)) {
             return 3;
         } else {
             return -1;
@@ -141,8 +141,6 @@ utf8_validate(unsigned char* data, size_t size)
             return -1;
         } else if(ui >= 0xD800 && ui <= 0xDFFF) {
             return -1;
-        } else if(ui == 0xFFFE || ui == 0xFFFF) {
-            return -1;
         } else if(ui > 0x10FFFF) {
             return -1;
         }
@@ -193,7 +191,7 @@ unicode_to_utf8(int c, unsigned char* buf)
         buf[1] = (unsigned char) 0x80 + (c & 0x3F);
         return 2;
     } else if(c < 0x10000) {
-        if(c < 0xD800 || (c > 0xDFFF && c < 0xFFFE)) {
+        if(c < 0xD800 || (c > 0xDFFF)) {
             buf[0] = (unsigned char) 0xE0 + (c >> 12);
             buf[1] = (unsigned char) 0x80 + ((c >> 6) & 0x3F);
             buf[2] = (unsigned char) 0x80 + (c & 0x3F);

test/004-strings.t

@@ -6,7 +6,7 @@ main([]) ->
     code:add_pathz("ebin"),
     code:add_pathz("test"),
 
-    etap:plan(119),
+    etap:plan(115),
     util:test_good(good()),
     util:test_good(uescaped(), [uescape]),
     util:test_errors(errors()),
@@ -29,7 +29,9 @@ good() ->
             <<"\"\\uD834\\uDD1E\"">>,
             <<240, 157, 132, 158>>,
             <<34, 240, 157, 132, 158, 34>>
-        }
+        },
+        {<<"\"\\uFFFF\"">>, <<239,191,191>>, <<34,239,191,191,34>>},
+        {<<"\"\\uFFFE\"">>, <<239,191,190>>, <<34,239,191,190,34>>}
     ].
 
 uescaped() ->
@@ -54,8 +56,6 @@ errors() ->
         <<"\"foo">>,
         <<"\"", 0, "\"">>,
         <<"\"\\g\"">>,
-        <<"\"\\uFFFF\"">>,
-        <<"\"\\uFFFE\"">>,
         <<"\"\\uD834foo\\uDD1E\"">>,
         % CouchDB-345
         <<34,78,69,73,77,69,78,32,70,216,82,82,32,70,65,69,78,33,34>>
@@ -88,10 +88,6 @@ utf8_cases() ->
         {<<16#C2, 16#81, 16#80>>, <<16#C2, 16#81, 16#EF, 16#BF, 16#BD>>},
         {<<"foo", 16#80, "bar">>, <<"foo", 16#EF, 16#BF, 16#BD, "bar">>},
 
-        % Invalid Unicode code points
-        {<<239, 191, 190>>, <<16#EF, 16#BF, 16#BD>>},
-        {<<237, 160, 129>>, <<16#EF, 16#BF, 16#BD>>},
-
         % Not enough extension bytes
         {<<16#C0>>, <<16#EF, 16#BF, 16#BD>>},